Reciprocating piston lubrication pump

ABSTRACT

A reciprocating piston lubrication pump with a component is proposed having an opening, which has at least one cylinder-shaped part, and with at least one piston, which comprises a radially outer surface built at least partly by a coating. A clearance between the radially outer surface of the piston and the component is between 1 μm and 20 μm when the radially outer surface is positioned in the cylinder-shaped part. The surface hardness of the coating at the radially outer surface is 2 to 10 times higher than that of a region of the component, which forms the cylinder-shaped part.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Patent Application no. 102020134539.9, filed Dec. 22, 2020, the contents of which is fully incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to a reciprocating piston lubrication pump with a component having an opening. This invention further relates to a reciprocating piston lubrication pump with a component having an opening that provides at least one cylinder-shaped part, and with at least one piston, which comprises a radially outer surface built at least partly by a coating.

BACKGROUND OF THE INVENTION

Lubrication pumps play a major role in lubrication systems. There are many different types of lubrication pumps such as reciprocating piston pump, rotary pump (screw, gear pumps, rotary vane and lobe pumps), eddy (slurry) pumps, etc. aiming for different application purposes. The reciprocating piston pump is one of the most often used pumps due to its compactness and precision of lubricant delivery. The lubrication pump can be used to deliver complicated lubricants to provide combination effects of anti-friction, anti-noise and even a sealing effect in the applications such as railroad, tunnel boring, mining, et al. To achieve the desired functions, the special lubricants however consist of a large amount of metallic particles, up to 30 wt % in total, in which iron, aluminum, copper and magnesium are the major compositions. In some cases, the lubricant may also have very low oil content, down to 35 wt %. The high content of the metallic particles and/or the low concentration of oils in the lubricants may accelerate the wear and induce local fracture of the pump components, i.e., pump piston and pump cylinder, and reduce the pump service life significantly. In some extreme cases, the pump may fail in few weeks and even in few days.

From the prior art a reciprocating piston lubrication pump is known with a valve, a piston and a cylinder, which comprises suction holes. During operation lubricant flows through the suction holes inside the cylinder. Afterwards the piston pumps the lubricant through the valve.

The task of the invention is in particular to provide a reciprocating piston lubrication pump with an efficient design and a high service life.

SUMMARY OF THE INVENTION

Suggested is a reciprocating piston lubrication pump with a component comprising an opening, which has at least one cylinder-shaped part, and with at least one piston, which comprises a radially outer surface built at least partly by a coating, wherein a clearance between the radially outer surface of the piston and the component is between 1 μm and 20 μm, preferably between 2 μm and 10 μm, when the radially outer surface is positioned in the cylinder-shaped part, wherein the surface hardness of the coating at the radially outer surface is 2 to 10 times higher, preferably 4 to 8 times higher, than that of a region of the component, which forms the cylinder-shaped part. Through this an efficient design and a high service life can be achieved. In particular little wear and little occurrence of fracture damage during operation, in particular for lubricants with a high percentage of metallic particles and/or low oil content, can be attained for relatively low costs.

Preferably at least the region of the component consists of a steel, which comprises 0.8 to 1.5 weight percent of Carbon, 4.0 to 5.0 weight percent of Chromium, 1.5 to 4.5 weight percent of Vanadium, 5.5 to 6.5 weight percent of Tungsten and 4.5 to 5.5 weight percent of Molybdenum and 0.1 to 0.5 weight percent of Silicon. By this a high hardness of the region can be achieved in a cost efficient way.

Furthermore, it is suggested that at least the region of the component is hardened to a hardness of 700 to 900 HV, preferably of 750 HV to 850 HV, at room temperature and/or to an unnotched Izod toughness of 35 to 80 J, preferably of 50 to 70 J, at room temperature. The unnotched Izod toughness is the physical quantity measured according to the Standard D4812-19 of the American Society for Testing and Materials. Alternatively, a quantification could be given through the standard ISO 180. In combination with the hardness of the piston this minimizes the wear for lubricants with many metallic particles and a low oil content.

With advantage a radially inner surface of the region of the component is machined to a roughness R_(z)=2 to 6 μm. This implies a low friction with the piston and can be achieved in a cost saving manner.

Moreover, it is suggested that the coating is created by Physical Vapor Deposition and/or Chemical Vapor Deposition in a low vacuum chamber, which ensures an easy produceability.

Preferably at least a part of the coating consists of titanium carbonitride. Advantageously in this case the hardness is 2000 to 5000 HV, more preferably between 3000 and 4000 HV.

Moreover, it is suggested that at at least a part of the coating consists of TiAlSiN and/or TiSiN and/or AlCrN. Advantageously in this case the hardness is 3000 to 6000 HV, preferably between 4000 and 5500 HV.

Preferably the coating has a thickness between 1 and 12 μm and more preferably between 2 μm and 6 μm.

With advantage at least a part of the piston consists of steel, which comprises 0.8 to 1.0 weight percent of Carbon, 4.0 to 4.5 weight percent of Chromium, 1.5 to 2.5 weight percent of Vanadium, 5.5 to 6.5 weight percent of Tungsten and 4.5 to 5.5 weight percent of Molybdenum and 0.1 to 0.5 weight percent of Silicon. Thereby the required hardness can be achieved very economically.

Moreover, it is suggested that the piston comprises a hardness between 650 and 850 HV, preferably between 700 HV and 800 HV, at room temperature and/or an unnotched Izod toughness between 50 and 80 J, preferably between 60 and 70 J, at room temperature. In combination with the hardness of the region of the component this minimizes the wear for lubricants with many metallic particles and a low oil content.

The piston can be hardened and tempered at temperatures between 450 and 600° C.

Preferably a base body of the piston retains dimensional stability up to 500° C., which implies that it is tolerant to the thermal impact during the coating deposition process.

Advantageously the coating is machined to a roughness R_(z)=1 to 5 μm. This implies a low friction with the piston and can be achieved in a cost saving manner.

Moreover, it is suggested that the piston is made of a high carbon and low alloyed steel, which can retain the dimensional stability up to 500° C. Preferably a critical load L_(c) of the coating and/or an adhesion of the coating to a base body of the piston is equal or higher than 30 N, preferably higher than 50 N, measured according to the standard ISO 20502 and/or according to the standard EN 1071-3 and/or according to the standard ASTM C1624. By this a high resistibility in particular against metallic particles in the lubricant can be attained.

There can be a chamfer on the piston front. The angle of the chamfer can be 15 to 75° and preferably 30 to 60°, the length of the chamfer can be 0.2 to 4 mm, preferably 0.5 to 2 mm A minimization of negative interaction with metallic particles of the lubricant can be attained. A surface roughness on the chamfer can be R_(z)=1 to 6 μm.

Furthermore, a device with the reciprocating piston lubrication pump is suggested, wherein the reciprocating piston lubrication pump contains a lubricant with more than 34 weight percent of oils and less than 60 weight percent, preferably less than 50 weight percent and more preferably less than 40 weight percent, of oils. Thereby a long service life of the reciprocating piston lubrication pump can be achieved despite the special kind of lubricant.

Furthermore, a device with the reciprocating piston lubrication pump is suggested, wherein the reciprocating piston lubrication pump contains a lubricant with more than 10 weight percent, preferably more than 18 weight percent and more preferably more than 25 weight percent of metallic particles. Thereby a long service life of the reciprocating piston lubrication pump can be achieved despite the special kind of lubricant.

BRIEF DESCRIPTION OF THE FIGURES

Further advantages result from the following drawing description. The drawings show an embodiment of the invention. The drawings, the description and the claims contain numerous features in combination. It is advisable for the person skilled in the art to consider the features individually and to combine them into meaningful further combinations.

FIG. 1 shows an axial local section of a reciprocating piston lubrication pump according to the invention,

FIG. 2 shows an axial section of a component of the reciprocating piston lubrication pump,

FIG. 3 shows a side view of a piston of the reciprocating piston lubrication pump,

FIG. 4 shows a view on the component in axial direction.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an axial local section of a reciprocating piston lubrication pump 10 according to the invention, which comprises component 12 with an opening 14 (FIG. 2). The opening 14 has a cylinder-shaped part 16. A piston 18 of the reciprocating piston lubrication pump 10 is located partly within a region 24 of the component, which forms the cylinder-shaped part 16. The piston 18 has a radially outer surface 20 which is built by a coating 22. A clearance between the radially outer surface of the piston and the component is between two and 10 micrometers when the radially outer surface is located in the cylinder-shaped part. A surface hardness of the coating at the radially outer surface is four to eight times higher than that of the region of the component which forms the cylinder-shaped part.

The component comprises a hole 30 (FIG. 1) and a further hole (not shown) through which lubricant (not shown) is sucked into a part of the opening, which is located between the piston and a valve 26 of the reciprocating lubrication pump, when the piston is moving away from the valve during operation. Afterwards the piston is moving towards the valve 26 and causes the lubricant to be pressed through the valve and afterwards through a hole 32 (FIG. 2) of the component 12. The valve 26 is a check valve. When the piston is moved fully towards the valve 26 a spring 28 of the reciprocating lubrication pump 10 pushes the piston back and away from the valve 26.

In different embodiments the component can have different numbers of holes through which lubricant is sucked in, e. g. three or four.

The component consists of a steel, which comprises 0.8 to 1.5 weight percent of Carbon, 4.0 to 5.0 weight percent of Chromium, 1.5 to 4.5 weight percent of Vanadium, 5.5 to 6.5 weight percent of Tungsten and 4.5 to 5.5 weight percent of Molybdenum and 0.1 to 0.5 weight percent of Silicon. Furthermore, the region of the component is hardened to a hardness of 750 to 850 HV at room temperature and to an unnotched Izod toughness of 50 to 70 J at room temperature. A radially inner surface of the region of the component is machined to a roughness R_(z)=2 to 6 μm.

The coating 22 of the piston consists of titanium carbonitride and has a thickness between 2 and 6 μm. The piston consists of a base body and the coating. The base body of the piston consists of steel, which comprises 0.8 to 1.0 weight percent of Carbon, 4.0 to 4.5 weight percent of Chromium, 1.5 to 2.5 weight percent of Vanadium, 5.5 to 6.5 weight percent of Tungsten and 4.5 to 5.5 weight percent of Molybdenum and 0.1 to 0.5 weight percent of Silicon.

The base body of the piston comprises a hardness between 700 and 800 HV at room temperature and an unnotched Izod toughness between 60 and 70 J at room temperature. The coating comprises a hardness between 3000 HV and 4000 HV. The radially outer surface of the piston, which is built by the coating, has a roughness R_(z) between 1 and 5 μm. A critical load Le of the coating and an adhesion of the coating to the base body of the piston is equal or higher than 30 N measured according to the standard ISO 20502.

During an operation in a device the reciprocating piston lubrication pump contains a lubricant with more than 34 weight percent of oils and less than 50 weight percent of oils and with more than 18 weight percent of metallic particles.

There is a chamfer 34 on the piston front. The angle of the chamfer is 30 to 60° measured relative to a central axis 36, and the length is 0.5 to 2 mm, and the surface roughness on the chamfer is R_(z)=1 to 6 μm.

In comparison to a conventional pump in which the piston and the cylinder are made of machinable hardened steel, the described pump, in which the piston and the component are made of the special steels and coatings, can prolong the pump service life by 4 to 100 times when pumping a special lubricants consisting of high metallic particles and/or low oil. Abrasive wear and fracture induced by metallic particles and poor lubrication induced by starved lubrication due to low oil content on the piston and the surface of the region can be minimized by the special steels and the coating, which have higher hardness, high toughness and optimized matching of the hardness between the piston coating and the surface of the region of the component. 

1. A reciprocating piston lubrication pump with a component comprising: an opening, which has at least one cylinder-shaped part, and with at least one piston, which comprises a radially outer surface built at least partly by a coating, wherein a clearance between the radially outer surface of the piston and the component is between 1 μm and 20 μm when the radially outer surface is positioned in the cylinder shaped part, and wherein the surface hardness of the coating at the radially outer surface is 2 to 10 times higher than that of a region of the component, which forms the cylinder-shaped part.
 2. The reciprocating piston lubrication pump according to claim 1, wherein at least the region of the component consists of a steel, which comprises 0.8 to 1.5 weight percent of Carbon, 4.0 to 5.0 weight percent of Chromium, 1.5 to 4.5 weight percent of Vanadium, 5.5 to 6.5 weight percent of Tungsten and 4.5 to 5.5 weight percent of Molybdenum and 0.1 to 0.5 weight percent of Silicon.
 3. The reciprocating piston lubrication pump according to claim 1, wherein at least the region of the component is hardened to a hardness of 700 to 900 HV at room temperature and/or to an unnotched Izod toughness of 35 to 80 J at room temperature.
 4. The reciprocating piston lubrication pump according to claim 1, wherein a radially inner surface of the region of the component is machined to a roughness R_(z)=2 to 6 μm.
 5. The reciprocating piston lubrication pump according to claim 1, wherein at least a part of the coating consists of titanium carbonitride and/or TiAlSiN and/or TiSiN and/or AlCrN.
 6. The reciprocating piston lubrication pump according to claim 1, wherein the coating has a thickness between 1 and 12 μm.
 7. The reciprocating piston lubrication pump according to claim 1, wherein at least a base body of the piston consists of steel, which comprises 0.8 to 1.0 weight percent of Carbon, 4.0 to 4.5 weight percent of Chromium, 1.5 to 2.5 weight percent of Vanadium, 5.5 to 6.5 weight percent of Tungsten and 4.5 to 5.5 weight percent of Molybdenum and 0.1 to 0.5 weight percent of Silicon.
 8. The reciprocating piston lubrication pump according to claim 1, wherein the piston comprises a hardness between 650 and 850 HV at room temperature and/or an unnotched Izod toughness between 50 and 80 J at room temperature.
 9. The reciprocating piston lubrication pump according to claim 1, wherein the coating is machined to a roughness R_(z)=1 to 5 μm.
 10. The reciprocating piston lubrication pump according to claim 1, wherein a critical load L_(c) of the coating and/or an adhesion of the coating to a base body of the piston is equal or higher than 30 N measured according to the standard ISO 20502 and/or according to the standard EN 1071-3 and/or according to the standard ASTM C1624.
 11. A device with a reciprocating piston lubrication pump comprising: a reciprocating piston lubrication pump with a component comprising: an opening, which has at least one cylinder-shaped part, and with at least one piston, which comprises a radially outer surface built at least partly by a coating, wherein a clearance between the radially outer surface of the piston and the component is between 1 μm and 20 μm when the radially outer surface is positioned in the cylinder shaped part, and wherein the surface hardness of the coating at the radially outer surface is 2 to 10 times higher than that of a region of the component, which forms the cylinder-shaped part, wherein the reciprocating piston lubrication pump contains a lubricant with more than 34 weight percent of oils and less than 60 weight percent, preferably less than 50 weight percent and more preferably less than 40 weight percent of oils.
 12. The device, in particular according to claim 11, wherein the reciprocating piston lubrication pump contains a lubricant with more than 10 weight percent, preferably more than 18 weight percent and more preferably more than 25 weight percent of metallic particles. 